1. Field of the Invention
The present invention relates to semiconductor devices. More specifically, it relates to heat removal in semiconductor devices.
2. Description of the Related Art
The advent of semiconductor devices and the analogue and digital functions enabled by them have revolutionized many contemporary industries and improved the general quality of life for many people. As technology has become increasingly more refined and developed, the performance requirements placed on semiconductor devices in order to implement this technology have also increased.
In Very Large Scale Integration (VLSI) integrated circuits, thousands or even millions of semiconductor devices such as transistors may be built on a common substrate. These semiconductor devices generally produce heat energy when they are conducting current or switching between states. As device size has decreased and more and more semiconductor devices are being fabricated on chips, the issue of heat removal from the integrated circuits has become a greater concern. Semiconductor devices may be fabricated in very close proximity to other devices. As a result, heat produced by one device may adversely affect the performance of a neighboring device. Excessively high temperatures in an integrated circuit may cause voids to form in metal wiring or excessive amounts of leakage current. Both of these as well as other high-temperature related problems may lead to improper functionality or even failure of integrated circuits.
A heat sink is a good thermal conductor that aids in the dissipation of heat energy through the principles of conduction and convection. It is not uncommon for areas of greater heat concentration, or “hot spots,” to develop on the face of a semiconductor device. In order to improve heat transfer into a heat sink for dissipation, a heat spreader is often used in conjunction with a heat sink. Heat spreaders are thermally conductive interface elements that attach to both the semiconductor device face and the heat sink. Due to their high thermal conductivity, heat spreaders typically spread heat energy from the “hot spots” on a semiconductor device over their entire volume to more efficiently transfer the heat energy to the heat sink.
Several potential solutions to the problem of heat removal in an integrated circuit are known in the art. Many involve the use of one or more heat sinks and/or heat spreaders.
U.S. Pat. No. 6,333,557 to Sullivan, which is herein incorporated by reference for all it discloses, includes a system wherein one or more cooling posts, e.g., multiple thermally conductive plugs are selectively disposed within a semiconductor chip structure adjacent to one or more electrically conductive levels and thermally coupled thereto so that heat produced by conductive lines within the wiring levels is transferred into and through the cooling posts for forwarding to a supporting substrate, which may have a back surface coupled to a cold plate, or to an upper surface of the semiconductor chip structure.
U.S. Pat. No. 6,211,569 to Lou, which is herein incorporated by reference for all it discloses, teaches of a structure of metal interconnection lines in which a silicon nitride layer is formed underneath a first metal pattern of integrated circuits. A silicon nitride plug is formed between two adjacent metal patterns and it serves as a thermal conductor. At least one metal plug in the dielectric layers between the metal patterns is an electrical connection of the integrated circuits.
U.S. Pat. No. 5,955,781 to Joshi, et al., which is herein incorporated by reference for all it discloses, teaches a semiconductor chip structure with at least one thermal conductor embedded within the semiconductor chip structure, the thermal conductor providing electrical insulation and a plurality of devices formed within the structure adjacent to the thermal conductor such that during operation heat produced in the devices is transferred into and through the thermal conductor to reduce the operating temperature of the devices. The thermal conductor is preferably diamond deposited by vapor phase process (CVD). The device is preferably a silicon-on-insulator device. Diamond may also be deposited into channels cut or etched in the back of the substrate.
U.S. Pat. No. 5,621,616 to Owens, et al., which is herein incorporated by reference for all it discloses, teaches of a thermally conductive metal frame in one of the metallization layers that gathers heat produced in the circuit. A plug member penetrates through the layer of insulative material and extends into a hole formed in the semiconductor substrate. This plug member is in conductive heat transfer relation with the material of the semiconductor substrate, and connects thermally with a heat sink.